JP2003189460A - Protective circuit against overcurrent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protective circuit against an overcurrent which enables power cut or easy adjustment of the time of automatic return. <P>SOLUTION: This protective circuit detects the abnormal heating accompanying the overcurrent of an external electrical apparatus 3, and a resistance varying element 18a varies its resistance value. The bias voltage outputted from a bias voltage output circuit 18 changes too, according to it. Furthermore, a relay 13 is opened or closed, based on the switching control signal being supplied and controlled by the second transistor element 17, based on the change of this bias voltage. By such control, the power cut at abnormal heating accompanying the overcurrent or the automatic return at vanishing of abnormal heating becomes possible. This protective circuit against an overcurrent having such an automatic return function is not connected serially to a coil 13a unlike a conventional one, but is included in a bias voltage output circuit 18 which supplies a switching control signal for exciting the coil 13a. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit, and more particularly to an overcurrent protection circuit having an automatic recovery function for automatically returning from a power-off state due to an overcurrent to a normal state.

[0002]

2. Description of the Related Art In recent years, a variety of electric equipments having an on-vehicle battery as a driving power source are mounted on a vehicle. Then, based on the detection of abnormal heat generation due to overcurrent of this electrical equipment, it automatically shuts off the power supply to the electrical equipment, and when the abnormal heat disappears, it can automatically return to the normal state. An overcurrent protection circuit having a function is known.
This power supply cutoff or automatic recovery is performed by controlling the opening and closing of a relay including a coil, but according to the conventional example, a current equivalent to the current flowing through the coil flows through the temperature detecting element for detecting the abnormal heat generation. Therefore, there is a problem that it is difficult to cut off the power supply and adjust the time for automatic recovery. A conventional example having such a problem will be described below with reference to FIG.

FIG. 4 is a circuit diagram showing an example of a conventional overcurrent protection circuit. Here, the overcurrent protection circuit has been
The description will be made assuming that it is incorporated in a functional circuit built-in type electrical junction box called a junction block that is often used for vehicles.

The electric junction box 9 shown in FIG. 4 is mounted on a vehicle, and the battery 2 is connected to its power input terminal 91 and external output terminal 92.
And the motor 3 are connected. The battery 2 is, for example, a known 12V system battery, and the motor 3 is, for example, a motor for driving a fan for engine cooling. This motor 3 is provided with two power supply terminals 3a and 3c and two ground terminals 3b and 3d.
It is a well-known four-terminal type whose rotation speed is variable by a drive signal supplied to c. For example, the power supply terminal 3a
Alternatively, when power is supplied to one of the terminals 3c and 3c, the motor rotates at low speed, and when power is supplied to both terminals 3a and 3c, the motor rotates at high speed. Therefore, it is assumed that power is supplied to both terminals 3a and 3c at the same time.

The electric junction box 9 accommodates various electronic parts and resin parts therein, and is provided with a bus bar which is a conductive plate for distributing the electric power supplied from the battery 2. . Then, in the vicinity of this bus bar, a PTC (positive temperature coefficient thermistor) as a temperature detecting element is provided.
93 is arranged, and the overcurrent flowing through the bus bar is detected based on the temperature monitoring by the PTC 93. In the electric connection box 9, a coil 97a excited by a predetermined current opens and closes a contact 97b, so that the battery 2
Is equipped with a relay 97 for controlling the power supply to the motor 3. Furthermore, the electric connection box 9 receives an external control signal input from the signal input terminal 94 to receive a relay 97.
CPU95 that outputs a switching control signal to control opening and closing
Is also equipped.

In such a configuration, for example, when an ignition switch (not shown) is turned on, an external control signal is input to the CPU 95 via the signal input terminal 94. In response to this, the CPU 95 outputs a high level signal to turn on the transistor element 96. At the same time, the relay 9 from the battery 2 via the power input terminal 91.
A current flows through the coil 97a of No. 7 and the contact 97b is closed. As a result, the current from the battery 2 is transferred to the relay 9
It is supplied to the power supply terminals 3a and 3c of the motor 3 via the contact point 97b of 7 and the external output terminal 92. This brings the motor 3 into operation.

In this operating state, for example, assuming that the vehicle travels on a submerged road, in this case, the fan driven by the motor 3 is locked or in a state close to this due to flooding. However, since the motor 3 tries to continue driving even against the resistance force of water, an overcurrent called a lock current flows. That is, an overcurrent also flows through the bus bar, and the bus bar abnormally heats up with this. Due to this abnormal heat generation, the PTC 93 rapidly increases its resistance value, so that no current flows through the coil 97a of the relay 97. As a result, the relay 97
Since the contact 97b of 1 is opened and the current supply to the motor 3 is also stopped, the overcurrent disappears and the temperature of the bus bar is lowered accordingly, and the electronic parts and resin parts, and further the motor 3 are protected.

On the other hand, if the current supply to the motor 3 is stopped, the cooling effect of the engine cannot be obtained.
When the running of the submerged road is finished and the temperature is sufficiently lowered, the driving of the motor 3 is restarted by the action opposite to the above.
That is, when the current supply is stopped and the temperature of the bus bar also drops sufficiently, the resistance value of the PTC 93 decreases and the relay 97
Current again flows through the coil 97a. As a result, the contact 97b of the relay 97 is closed and the current supply to the motor 3 is restarted, so that the motor 3 is restarted. Thus, this conventional example also has an automatic return function. In this conventional example, it is assumed that sufficient waterproof measures are taken.

[0009]

By the way, since the shape and type of the bus bar and the type of external electrical equipment for on / off control are not always uniform, it is necessary to select a PTC 93 having a temperature characteristic suitable for them. There is. However, according to the above conventional example, the PTC 93 and the coil 97
Since it is connected in series with a, a passing current equivalent to that of the coil 97a flows through the PTC 93. Therefore, in the conventional example, in order to adjust the time or timing of power shutoff or automatic recovery according to the shape and type of the bus bar or the type of external electrical equipment, P
TC93 should be selected. That is, the choice of the PTC 93 depends on the passing current of the coil 97a. Therefore, according to the conventional example, it has been difficult to adjust the required power-off time or automatic recovery time. In particular, a PTC 93 equivalent to the passing current of the coil 97a
When selecting (1), since a relatively large capacity PTC 93 is required, it is often impossible to satisfy the space constraint in the electric box, which tends to increase the density.

In view of the above situation, it is an object of the present invention to provide an overcurrent protection circuit capable of easily adjusting the time for shutting off the power supply or automatically returning.

[0011]

The overcurrent protection circuit according to claim 1, which is made to solve the above-mentioned problems, has a driving power source 2 and an external electric equipment 3 which are connected to the input and output ends thereof, respectively. A coil 13a excited by a passing current opens and closes a contact 13b, and is an overcurrent protection circuit connected to a relay 13 for controlling power supply from the driving power source 2 to the external electrical equipment 3, which is the coil. First transistor element 16 which is connected in series to 13a and controls the current flowing through the coil 13a in response to a predetermined switching control signal, and abnormal heat generation when an overcurrent flows through the external electrical equipment 3. And a variable resistance element 18a, which is arranged in a region that is a temperature detection target for detecting the temperature, and has a characteristic that its resistance value changes in accordance with a temperature change.
a bias voltage adjusting resistor 18b connected in series to a, and a bias voltage output circuit 18 for dividing the applied voltage from the bias power source + B and outputting the bias voltage by the resistance variable element 18a and the bias voltage adjusting resistor 18b. And a second controlling the supply of the switching control signal to the first transistor element 16 based on the bias voltage.
The transistor element 17 is included.

According to the first aspect of the invention, the resistance variable element 1 is detected by detecting abnormal heat generation due to overcurrent of the external electrical equipment 3.
8a changes its resistance value. In response to this, the bias voltage output from the bias voltage output circuit 18 also changes. Further, the relay 13 is controlled to open / close based on the switching control signal supplied and controlled by the second transistor element 17 based on the change in the bias voltage. By such control, it is possible to shut off the power supply when abnormal heat is generated due to overcurrent and to automatically recover when the abnormal heat disappears. In the present overcurrent protection circuit having such an automatic recovery function, the variable resistance element 18a is not connected in series to the coil 13a as in the conventional case, but a switching control signal for exciting the coil 13a is supplied. It is included in the bias voltage output circuit 18. In particular, the variable resistance element 18a is connected in series to the bias voltage adjusting resistance 18b. Therefore, by appropriately selecting the bias voltage adjusting resistor 18b, it becomes possible to select the variable resistance element 18a that does not depend on the passing current of the coil 13a.

According to another aspect of the present invention, there is provided an overcurrent protection circuit according to claim 1, wherein the resistance variable element 18a has a secondary resistance value as the temperature rises. PT with curve-increasing properties
C18a, one end of this PTC18a is grounded,
The other end is connected to one end of the bias voltage adjusting resistor 18b, and the other end of the bias voltage adjusting resistor 18b is connected to the bias power source + B to configure the bias voltage output circuit 18. To do.

According to the second aspect of the invention, as the resistance variable element 18a, the PTC 18a having the characteristic that its resistance value increases in a quadratic curve is used. Such a PTC
By positively utilizing the resistance characteristic of 18a, it is possible to surely cope with a rapid temperature rise of the temperature detection target portion.

According to another aspect of the present invention, there is provided an overcurrent protection circuit according to the second aspect, wherein the PTC 18a is the temperature detection target portion of the overcurrent protection circuit. It is necessary to detect the temperature of the bus bar 20 by contacting the bus bar 20 arranged between the power source 2 and the external electric equipment 3 and electrically connected to the driving power source 2 and the external electric equipment 3. Characterize.

According to the invention of claim 3, the PTC18
Since a is in contact with the bus bar 20 arranged between the drive power source 2 and the external electric equipment 3 to detect its temperature, it is possible to reliably detect the overcurrent. .

The overcurrent protection circuit according to claim 4 made to solve the above-mentioned problems is the overcurrent protection circuit according to claim 3, wherein both the first transistor element 16 and the second transistor element 17 are emitters. Grounded NPN
Type transistor element, the collector of the second transistor element 17 is connected to the base of the first transistor element 16 and is generated in response to an external control signal for controlling the operation of the external electrical equipment 3. Further, the switching control signal is supplied, and one end of the coil 13a is connected to the collector of the first transistor element 16.

According to the fourth aspect of the invention, both the first transistor element 16 and the second transistor element 17 are NPN type transistor elements whose emitters are grounded, and the base of the first transistor element 16 is the second transistor element 17. Since the collector is connected and the external control signal is supplied and one end of the coil 13a is connected to the collector, a highly versatile overcurrent protection circuit can be obtained with a simple circuit configuration.

According to another aspect of the present invention, there is provided an overcurrent protection circuit according to claim 4, wherein the switching control signal is in the off state of the second transistor element 17. Sometimes, it is a high level signal supplied to the first transistor element 16.

According to the fifth aspect of the present invention, the switching control signal is a high level signal supplied to the first transistor element 16 when the second transistor element 17 is in the off state. It becomes possible to control the opening / closing of the relay 13, that is, the power supply control of the external electrical equipment 3.

According to a sixth aspect of the present invention, there is provided an overcurrent protection circuit according to the fifth aspect, wherein the overcurrent protection circuit is a vehicle-mounted overcurrent protection circuit. Is a motor 3 which constitutes a radiator cooling fan driven by being supplied with power from a vehicle-mounted battery 2 as the driving power source 2.

According to the sixth aspect of the invention, it is possible to detect abnormal heat generation due to overcurrent of the motor 3 which constitutes the radiator cooling fan of the vehicle. That is, the motor that constitutes the radiator cooling fan can be a main cause of abnormal heat generation of the connected bus bar 20.
The present invention surely detects such abnormal heat generation and controls power supply. Therefore, according to the present invention, it is possible to reliably prevent damage to the electronic circuit parts related to the motor drive in the vehicle and the resin parts such as the resin plate.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B are circuit diagrams showing an overcurrent protection circuit according to an embodiment of the present invention. As shown in FIG. 1A, the overcurrent protection circuit is
For example, the present invention is applied to a motor drive electrical junction box 1 which is one of functional circuit built-in electrical junction boxes. The electric connection box 1 for driving a motor is mounted on a vehicle, and a battery 2 (corresponding to a driving power supply in the claims) and a motor 3 (external electrical equipment in the claims) are provided in a power input terminal 11 and an external output terminal 12, respectively. Equivalent to equipment) is connected. As described above, the battery 2 is, for example, a well-known 12V battery,
The motor 3 is, for example, a motor for driving a fan for cooling the engine. As described above, the motor 3 has two power supply terminals 3a and 3c and two ground terminals 3
This is a well-known four-terminal type which is provided with b and 3d and whose rotation speed is variable by a drive signal supplied to the power supply terminals 3a and 3c. For example, when power is supplied to either one of the power supply terminals 3a or 3c, it rotates at a low speed, and when power is supplied to both terminals 3a and 3c, it rotates at a high speed. , Both terminals 3a and 3c are simultaneously supplied with power.

The motor drive electrical junction box 1 accommodates various electronic components and resin components therein, and is provided with a bus bar which is a conductive plate for distributing the electric power supplied from the battery 2. ing. This bus bar will be described later with reference to FIG. A temperature detecting element such as a PTC (Positive Characteristic Thermistor) is arranged so as to come into contact with the bus bar, and abnormal heat generation, that is, an overcurrent is detected using this temperature detecting element.

Further, in the motor drive electric junction box 1, a coil 13a excited by a predetermined passing current is provided with a contact 13.
A relay 13 that controls the power supply from the battery 2 to the motor 3 by opening and closing b is provided. In addition, a high level signal (corresponding to the external control signal in the claims) for receiving an external control signal input from the signal input terminal 14 and controlling the opening / closing of the relay 13 in the motor drive electrical junction box 1. CPU15 which outputs is also equipped.

Further, in the motor drive electrical junction box 1, a first transistor element 16 and a second transistor element 17 which constitute an overcurrent protection circuit, and a bias voltage output circuit 18 are provided.
It is included. The first transistor element 16 is connected in series to the coil 13a of the relay 13 and controls the current flowing through the coil 13a in response to the switching control signal. Specifically, the emitter of the first transistor element 16 is grounded, one end of the coil 13a is connected to its collector, and the switching control signal is supplied to its base.

The bias voltage output circuit 18 comprises a PTC 18a and a bias voltage adjusting resistor 18b which are connected in series. The PTC 18a is arranged at a portion to be a temperature detection target for detecting abnormal heat generation when an overcurrent flows due to the lock of the motor 3 or the like. For details, see this P
As described above, the TC 18a is arranged so as to come into contact with, for example, the bus bar which is routed between the battery 2 and the motor 3 and electrically connected thereto. This PTC
Reference numeral 18a is, for example, a known positive temperature coefficient thermistor having a characteristic that the resistance value increases in a quadratic curve as the temperature rises. In order to effectively utilize this resistance change of the positive characteristic, one end of the PTC 18a is grounded here. On the other hand, the bias voltage adjusting resistor 1 connected in series to the PTC 18a
8b divides the voltage applied from the bias power source + B and outputs the bias voltage from the connection point with the PTC 18a. The PTC 18a corresponds to the variable resistance element in the claims.

As described above, the PTC 18a having the characteristic that the resistance value increases in a quadratic curve as the temperature rises is connected and used as shown in FIG.
By positively utilizing the resistance characteristic of C18a, it becomes possible to surely cope with a rapid temperature rise of the portion to be the temperature detection target. Instead of the PTC 18a, it is possible to use an ordinary thermistor having a characteristic that the resistance value decreases with an increase in temperature. However, in this case, the connection relationship between the thermistor and the bias voltage adjusting resistor is as shown in FIG.
The PTC 18a and the bias voltage adjusting resistor 18 shown in FIG.
The connection relationship with b is opposite. That is, the bias power source + B is connected to one end of the thermistor, and the bias voltage adjusting resistor is grounded.

Further, according to the above-described embodiment, both the first transistor element 16 and the second transistor element 17 are NPN type transistor elements whose emitters are grounded, and the base of the first transistor element 16 is the second transistor element 17. Since the collector is connected and an external control signal is supplied and one end of the coil 13a is connected to the collector, a highly versatile overcurrent protection circuit can be obtained with a simple circuit configuration.

In such a configuration, for example, when an ignition switch (not shown) is turned on, an external control signal is input to the CPU 15 via the signal input terminal 14. In response to this, the CPU 15 outputs the high level signal to the base side of the first transistor element 16 to turn on the first transistor element 16. At this time, if the second transistor element 17 is off, this high level signal is applied to the base of the first transistor element 16, so that the first transistor element 16 is turned on. That is, when the resistance value of the PTC 18a is low because the motor 3 is operating normally and the temperature of the bus bar is normal, the bias voltage is almost equal to the ground potential, so the second transistor element 17 is in the off state. As a result, current flows from the battery 2 to the coil 13a of the relay 13 via the power input terminal 11, and the contact 13b is closed. As a result, the current from the battery 2 is transferred to the contact 1 of the relay 13.
It is supplied to the power supply terminals 3a and 3c of the motor 3 via the 3b and the external output terminal 12. As a result, the motor 3 is put into operation. The timing at which the high level signal is output may be when the ignition switch is turned on.

On the other hand, assuming, for example, that the vehicle travels on a submerged road, in this case, the fan driven by the motor 3 will be locked or in a state close to this due to flooding. However, since the motor 3 tries to continue driving even against the resistance force of water, an overcurrent called a lock current flows. Then, an overcurrent also flows through the busbar connected to the busbar, which causes abnormal heat generation in the busbar. This abnormal fever is caused by the PT
Since the resistance value of C18a is increased, the bias voltage from the connection point is applied to the base of the second transistor element 17. Then, the second transistor element 17 turns on and the collector-emitter of the second transistor element 17 becomes conductive, so that the switching control signal from the CPU 15 cannot turn on the first transistor element 16. Therefore, no current flows through the coil 13a of the relay 13, so that the contact 97b of the relay 97 is opened and the current supply to the motor 3 is also stopped. As a result, the overcurrent disappears and the temperature of the bus bar also drops accordingly, and the electronic components, the resin components, and the motor 3 are protected.

However, if this state continues and the current supply to the motor 3 is stopped, the cooling effect of the engine cannot be obtained. Therefore, for example, when the running of the submergence route is finished and the temperature is sufficiently lowered. The motor 3 is restarted by the action opposite to the above. That is, when the current supply is stopped and the temperature of the bus bar is sufficiently lowered, the resistance value of the PTC 18a is reduced, the bias voltage is lowered, and the second transistor element 17 is turned off. Therefore, the first transistor element 16 is turned on again. To do. As a result, a current flows through the coil 13a of the relay 13, the contact 13b of the relay 13 is closed, the current supply to the motor 3 is restarted, and the motor 3 is restarted. Thus, this embodiment also has an automatic return function. In this embodiment, sufficient waterproofing measures are taken, and it is assumed that there is no electric leakage, short circuit, etc. due to water infiltration.

As described above, the embodiment shown in FIG. 1A has a power-off function at the time of abnormal heat generation due to overcurrent and an automatic recovery function at the time of disappearance of abnormal heat generation. Also, in this embodiment,
The PTC 18a is not connected to the coil 13a in series as in the conventional case, but is included in the bias voltage output circuit 18 which supplies a switching control signal for exciting the coil 13a. In particular, the PTC 18a is connected in series with the bias voltage adjusting resistor 18b. Therefore, by appropriately selecting the bias voltage adjusting resistor 18b, P which does not depend on the passing current of the coil 13a is obtained.
It becomes possible to select the TC 18a. Also, PTC
By adjusting the passing current of 18a in the steady state, preheating is performed to facilitate the trip (cutoff) state, or conversely, once the trip state occurs, the trip is continued until the power is turned off once. It is also possible not to recover from the state.

Further, according to the above embodiment, the high level signal generated by the CPU in response to the external control signal is the first level signal when the second transistor element 17 is in the off state.
Since the power is supplied to the transistor element 16, more realistic power supply control of the motor 3 becomes possible. The first transistor element 16 shown in FIG.
Is the first transistor element 1 as shown in FIG.
It may be 6 '. This first transistor element 16 '
Is a diode D1, D2 and a Zener diode ZD
1 and ZD2, and has a switching function similar to that of the first transistor element 16 of FIG.

FIG. 2 is an exploded perspective view of a motor drive electrical junction box 1 to which the above-mentioned overcurrent protection circuit is applied. Figure 2
As shown in FIG. 1, the electric drive connection box 1 for driving a motor includes a first bus bar 20, a wiring board 30, a second bus bar 40, a terminal plate cover 50, a bus bar in a housing formed by an upper cover 10 and a lower cover 70. Board connection terminal 5
1, a terminal plate 52, a main circuit board 60, an electronic component 61, an electronic component holder 62, a sub-circuit substrate 63, and other components are housed. As shown in FIG. 2, the main circuit board 6
0, the terminal plate 52, the terminal plate cover 50, the second bus bar 40, the wiring board 30, and the first bus bar 20 are stacked in this order.

The upper cover 10 is in the shape of a rectangular box made of resin and is open downward. On the upper surface thereof, a socket-like connector portion 10a is formed which is open upward for connectors, fuses, relays and the like. This connector part 1
Each of the terminals to be described later projects and is arranged to be housed inside the 0a. In addition, a plurality of lock claws 10b used when being integrated with the lower cover 70 are formed on the side surface of the upper cover 10.

In this example, a plurality of tab-shaped connector terminals 20a are erected on the first bus bar 20 so as to face upward. These connector terminals 20a become a part of the terminals housed and arranged in the connector portion 10a. Also, the PTC upper portion 20b, which is a portion corresponding to above the PTC.
A contact piece, which will be described later, is formed on this. The wiring board 30 is arranged below this.

A second bus bar 40 is stacked below the first bus bar 20 and the wiring board 30. The second bus bar 40 also has a configuration similar to that of the first bus bar 20,
A plurality of tab-shaped connector terminals 40a are erected upwardly and continuously. These connector terminals 40a also become part of the terminals housed and arranged in the connector portion 10a. In addition, from the second bus bar 40, the first bus bar 2
It is assumed that a contact piece such as 0 is not formed. The first bus bar 20 and the second bus bar 40 are strip-shaped and needless to say have conductivity.

Below the second bus bar 40, a terminal plate cover 50 and a terminal plate 5 for sandwiching and holding a plurality of bus bar board connecting terminals 51 from above and below.
2 are stacked. Also, the terminal plate cover 50
The terminal plate 52 is basically the main circuit board 6
It is made of resin in order to electrically insulate the 0 side and the bus bar side, and needless to say, the bus bar board connecting terminal 51 is conductive. Specifically, each bus bar board connection terminal 51 is
Here, they are mounted on a plurality of terminal holding portions formed on a terminal plate 52 (not shown), and are electrically contacted with the main circuit board 60 side on the back side of the terminal plate 52. Although not shown here, the terminal plate cover 50 also has a plurality of window portions at portions corresponding to the predetermined bus bar board connecting terminals 51 mounted on the terminal plate 52, and the bus bar is provided through these window portions. The board connecting terminal 51 is adhered to the terminal plate 52 so as to sandwich the bus bar board connecting terminal 51 so as to project upward.

A main circuit board 60 is stacked below the terminal plate 52. The relay 13, the regulator, an electronic component 61 such as a diode, and the PTC 18a are mounted on the main circuit board 60. Then, these electronic components 61 are covered with an electronic component holder 62 having a lower opening, and a sub circuit board 63 is mounted on the upper surface of the electronic component holder 62. This sub-circuit board 6
The CPU 15 and the like are mounted on the CPU 3. Also, FIG.
The overcurrent protection circuit shown in (A) is also mounted on the sub circuit board 63. However, the overcurrent protection circuit may be mounted on the main circuit board 60.

Then, the above-mentioned reference numerals 20, 30, 4
The component groups indicated by 0, 50 to 52, 60 to 63, etc. are housed in a resin-made rectangular lower cover 70. A plurality of lock holes 70 are provided on the side surface of the lower cover 70.
a is formed, the upper cover 10 is covered from above, and the plurality of lock holes 70a and the plurality of lock claws 10b engage with each other to integrate the upper cover 10 and the lower cover 70. It

FIG. 3 is a partially exploded perspective view for explaining the structure around the PTC window portion. As shown in FIG. 3, a contact piece 20c having a shape bent downward in an L-shaped cross section is provided at a side edge portion of the PTC upper portion 20b of the first bus bar 20.
Are integrally formed with the first bus bar 20. The contact piece 20c contacts the side surface of the PTC 18a.

The PTC 18a generates heat when an overcurrent flows through the bus bar and increases the resistance. Based on this phenomenon, the current flowing through the bus bar is reduced or cut off.
Circuit protection and resin member protection are performed. This current control is performed, for example, by controlling the opening / closing of the relay 13. The PTC 18a exemplifies a rectangular plate-shaped outer shape having a predetermined thickness, but it may be a generally known circular shape. Also, PTC18
A has a lead terminal 60a extending downward and soldered to the main circuit board 60.

The terminal plate cover 50 has a PT
The C window portion 50f is formed. Window part 50f for PTC
Is formed corresponding to the PTC 18a, and in particular, a notch 50f1 is formed on one side wall portion side thereof so that the contact piece 20c can be inserted therethrough. Further, a fin portion 50g having a shape that partially surrounds the PTC 18a when viewed from above is integrally formed with the terminal plate cover 50 on the other side wall portion of the PTC window portion 50f facing the cutout portion 50f1. As will be described later, the hinge portion 50g has a U-shaped cross section, and a protrusion 50g1 is formed at the tip thereof.

On the terminal plate 52, the PTC
A window portion 52f having the same shape as the window portion 50f is provided.
In addition, a terminal hole 60 into which the lead terminal 18a1 of the PTC 18a is inserted and soldered in the main circuit board 60.
a is formed.

The contact piece 20c is provided with the hinge portion 5
It is inserted into a clearance between 0 g (strictly speaking, the protrusion 50g1) and the notch 50f1 of the PTC window 50f. At this time,
Due to the elasticity of the hinge part 50g, the PTC 18a contacts the contact piece 2
It is pressed against 0c. As a result, the contact piece 20c, that is, the bus bar 20 that is the temperature detection target, comes into contact with the PTC 18a and the temperature is reliably detected.

As described above, according to the present embodiment, the coil 1 of the relay 13 is, of course, cut off the power source when abnormal heat is generated due to overcurrent and automatically restored when the abnormal heat disappears.
It is possible to select the PTC 18a that does not depend on the passing current of 3a. Therefore, it becomes possible to easily adjust the time for power-off or automatic recovery due to overcurrent. Moreover, the present embodiment is particularly effective when applied to an electric connection box mounted on a vehicle. In other words, there are many electric components inside the vehicle, such as the motor that constitutes the radiator cooling fan, which can be the main cause of heat generation.However, abnormal heat generation of such electric components is reliably detected and power supply control is performed. Since this is performed, it is possible to surely prevent damage to the electronic circuit components included in the electrical equipment and the resin components such as the resin plate due to abnormal heat generation while using any PTC.

The present invention is not limited to the shapes of the electrical equipment and the bus bar shown in the above embodiment, and may be other types of electrical equipment and bus bars of other shapes. Further, the type of variable resistance element included in the bias voltage output circuit and the connection relationship between the variable resistance element and the bias voltage adjusting resistor can be changed. Further, the NPN type transistor shown in the embodiment may be a PNP type transistor. The present invention also includes modified forms within the scope not departing from the gist of the present invention.

[0049]

As described above, according to the invention of claim 1, the variable resistance element 18a is not connected in series to the coil 13a as in the conventional case, but the coil 13a is used.
It is included in the bias voltage output circuit 18 which supplies a switching control signal for exciting. In particular, the variable resistance element 18a is connected in series to the bias voltage adjusting resistance 18b. Therefore, by appropriately selecting the bias voltage adjusting resistor 18b, it becomes possible to select the variable resistance element 18a that does not depend on the passing current of the coil 13a. As a result, it becomes possible to easily adjust the time for power-off or automatic recovery due to overcurrent.

According to the second aspect of the invention, as the resistance variable element 18a, the PTC 18a having the characteristic that its resistance value increases in a quadratic curve is used. Such a PT
By positively utilizing the resistance characteristic of C18a, it becomes possible to reliably cope with a rapid temperature rise of the temperature detection target portion.

According to the invention of claim 3, the PTC18
Since a is in contact with the bus bar 20 provided between the drive power source 2 and the external electrical equipment 3 to detect its temperature, it is possible to reliably detect the overcurrent.

According to the fourth aspect of the invention, both the first transistor element 16 and the second transistor element 17 are NPN type transistor elements whose emitters are grounded, and the base of the first transistor element 16 is the second transistor element 17. Since the collector is connected and the external control signal is supplied and one end of the coil 13a is connected to the collector, a highly versatile overcurrent protection circuit can be obtained with a simple circuit configuration.

According to the fifth aspect of the present invention, the switching control signal is a high level signal supplied to the first transistor element 16 when the second transistor element 17 is in the off state, so that it is more realistic. Open / close control of relay 13,
That is, it becomes possible to control the power supply of the external electrical equipment 3.

According to the sixth aspect of the present invention, it is possible to detect abnormal heat generation due to the overcurrent of the motor 3 which constitutes the radiator cooling fan of the vehicle. That is, the motor that constitutes the radiator cooling fan can be a main cause of abnormal heat generation of the connected bus bar 20.
The present invention surely detects such abnormal heat generation and controls power supply. Therefore, according to the present invention, any PT
While using C, it is possible to reliably prevent damage to the electronic circuit parts related to the motor drive and the resin parts such as the resin plate.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an overcurrent protection circuit according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of an electric connection box for driving a motor to which the present overcurrent protection circuit is applied.

FIG. 3 is a partially exploded perspective view for explaining a configuration around a PTC window portion.

FIG. 4 is a circuit diagram showing an example of a conventional overcurrent protection circuit.

[Explanation of symbols]

1 Motor drive electrical connection box 2 battery (power supply for driving) 3 motors (external electrical equipment) 13 relays 13a coil 13b contact 16 First transistor element 17 Second transistor element 18 Bias voltage output circuit 18a PTC (variable resistance element) 18b Bias voltage adjustment resistor

Claims (6)

[Claims] 1. A power supply for driving and an external electric device are respectively connected to the input and output ends, and a coil excited by a predetermined passing current opens and closes a contact to supply power from the driving power supply to the external electric device. An overcurrent protection circuit connected to a relay for controlling supply, the first transistor element being connected in series to the coil and controlling a current flowing through the coil in response to a predetermined switching control signal; A variable resistance element having a characteristic that its resistance value changes according to temperature change, the resistance variable element being arranged in a portion to be a temperature detection target for detecting abnormal heat generation when an overcurrent flows in the external electric equipment. A bias voltage adjusting resistor connected in series to the variable resistance element, and the bias voltage is divided by the variable resistance element and the bias voltage adjusting resistor to divide the applied voltage from the bias power supply. A bias voltage output circuit for outputting, based on the bias voltage, a first of the switching control signal
A second transistor element that controls supply to the transistor element, and an overcurrent protection circuit comprising: 2. The overcurrent protection circuit according to claim 1, wherein the resistance variable element is a PTC having a characteristic that its resistance value increases in a quadratic curve with temperature rise.
Has one end connected to the ground, the other end connected to one end of the bias voltage adjusting resistor, and the other end of the bias voltage adjusting resistor connected to the bias power source to form the bias voltage output circuit. Characteristic overcurrent protection circuit. 3. The overcurrent protection circuit according to claim 2, wherein the PTC is arranged between the drive power supply and the external electrical equipment as a portion to be the temperature detection target, and the drive power supply is provided. And an overcurrent protection circuit which detects the temperature of the bus bar by contacting the bus bar electrically connected to the external electric equipment. 4. The overcurrent protection circuit according to claim 3, wherein the first transistor element and the second transistor element are both emitter-grounded NPN type transistor elements, and the base of the first transistor element is the The collector of the second transistor element is connected and the switching control signal generated in response to an external control signal for controlling the operation of the external electrical equipment is supplied.
An overcurrent protection circuit, wherein one end of the coil is connected to the collector of the transistor element. 5. The overcurrent protection circuit according to claim 4, wherein the switching control signal is a high level signal supplied to the first transistor element when the second transistor element is in an off state. Characteristic overcurrent protection circuit. 6. The overcurrent protection circuit according to claim 5, wherein the overcurrent protection circuit is mounted on a vehicle, and the external electrical equipment is driven by being powered by an onboard battery as the driving power source. An overcurrent protection circuit, which is a motor that constitutes a fan.